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Date:   Fri, 16 Apr 2021 15:46:20 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     akpm@linux-foundation.org, christophe.leroy@csgroup.eu,
        linux-mm@kvack.org, mm-commits@vger.kernel.org,
        steven.price@arm.com, torvalds@linux-foundation.org
Subject:  [patch 10/12] mm: ptdump: fix build failure
Message-ID: <20210416224620.vDDxhwPBO%akpm@linux-foundation.org>
In-Reply-To: <20210416154523.3f9794326e8e1db549873cf8@linux-foundation.org>
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From: Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: mm: ptdump: fix build failure

	  CC      mm/ptdump.o
	In file included from <command-line>:
	mm/ptdump.c: In function 'ptdump_pte_entry':
	././include/linux/compiler_types.h:320:38: error: call to '__compiletime_assert_207' declared with attribute error: Unsupported access size for {READ,WRITE}_ONCE().
	  320 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
	      |                                      ^
	././include/linux/compiler_types.h:301:4: note: in definition of macro '__compiletime_assert'
	  301 |    prefix ## suffix();    \
	      |    ^~~~~~
	././include/linux/compiler_types.h:320:2: note: in expansion of macro '_compiletime_assert'
	  320 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
	      |  ^~~~~~~~~~~~~~~~~~~
	./include/asm-generic/rwonce.h:36:2: note: in expansion of macro 'compiletime_assert'
	   36 |  compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \
	      |  ^~~~~~~~~~~~~~~~~~
	./include/asm-generic/rwonce.h:49:2: note: in expansion of macro 'compiletime_assert_rwonce_type'
	   49 |  compiletime_assert_rwonce_type(x);    \
	      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	mm/ptdump.c:114:14: note: in expansion of macro 'READ_ONCE'
	  114 |  pte_t val = READ_ONCE(*pte);
	      |              ^~~~~~~~~
	make[2]: *** [mm/ptdump.o] Error 1

READ_ONCE() cannot be used for reading PTEs.  Use ptep_get() instead.  See
commit 481e980a7c19 ("mm: Allow arches to provide ptep_get()") and commit
c0e1c8c22beb ("powerpc/8xx: Provide ptep_get() with 16k pages") for
details.

Link: https://lkml.kernel.org/r/912b349e2bcaa88939904815ca0af945740c6bd4.1618478922.git.christophe.leroy@csgroup.eu
Fixes: 30d621f6723b ("mm: add generic ptdump")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Steven Price <steven.price@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/ptdump.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/ptdump.c~mm-ptdump-fix-build-failure
+++ a/mm/ptdump.c
@@ -111,7 +111,7 @@ static int ptdump_pte_entry(pte_t *pte,
 			    unsigned long next, struct mm_walk *walk)
 {
 	struct ptdump_state *st = walk->private;
-	pte_t val = READ_ONCE(*pte);
+	pte_t val = ptep_get(pte);
 
 	if (st->effective_prot)
 		st->effective_prot(st, 4, pte_val(val));
_